Saturday, June 14, 2008

Arctic thaw threatens Siberian permafrost

The permafrost belt stretching across Siberia to Alaska and Canada could start melting three times faster than expected because of the speed at which Arctic Sea ice is disappearing.

A study found that the effects of sea-ice loss – which reached an all-time record last summer – extend almost 1,000 miles inland to areas where the ground is usually frozen all year round.

The smaller the area of sea ice, the less sunlight is reflected and the more heat is absorbed. That means scientists expect a tripling in the rate of warming over the continental land mass surrounding the Arctic. "Our study suggests that, if sea ice continues to contract rapidly over the next several years, Arctic land warming and permafrost thaw are likely to accelerate," said David Lawrence of the US National Centre for Atmospheric Research in Boulder, Colorado.

Last September, the sea ice of the Arctic shrank to more than 30 per cent of its average extent for that time of the year. Meanwhile, air temperatures over the Arctic region rose by about 2C above the long-term average for the period 1978 to 2006.

Melting permafrost threatens to undermine the roads, oil pipelines and buildings that are built on the permanently frozen ground. It will also endanger the region's wildlife as well as triggering the possible release of the greenhouse gases locked in the soil, which would exacerbate global warming.

Dr Lawrence and researchers at National Snow and Ice Data Centre used computer models to analyse how the loss of sea ice could influence rising air temperatures and the melting of permafrost. They looked in particular at the creation of "taliks", which are patches of unfrozen ground sandwiched between layers of permanently frozen soil lower down and a seasonally frozen patch of soil above.

"Taliks form when the downwelling summer heating wave extends deeper than the corresponding winter cooling wave, thereby preventing the talik from refreezing in winter and permitting heat to accumulate at depth as soil ice melts," the scientists said in their study to be published in the journal Geophysical Research Letters.

Taliks allow heat to build up more quickly in the soil which increases the rate at which permafrost is subjected to a long-term thaw. "Taken together, these results imply a link between rapid sea ice loss and permafrost health," the scientists warned.

Dr Lawrence said that about a quarter of the northern hemisphere's land contains perma-frost and the Arctic region's soils are believed to hold about 30 per cent of all the carbon stored in the world's soil. "An important, unresolved question is how the delicate balance of life in the Arctic will respond to such a rapid warming," he said. "Will we see, for example, accelerated coastal erosion, or increased methane emissions, or faster shrub encroachment into tundra regions if sea ice continues to retreat rapidly?"

Andrew Slater, a co-author of the study, said: "The rapid loss of sea ice can trigger widespread changes that would be felt across the region."

Claire Parkinson of Nasa said the consequences of the loss of the permafrost were unknown. "They could be significant, both on the climate through release of greenhouse gases and on the local communities through damage to roads and buildings as the frozen ground underneath thaws and destabilises".